Bioconversion processes of carbohydrates to their cellular compounds have become increasingly important, providing a variety of advantages over non-biological conversion processes. Due to the abundant availability of natural resources for bioconversion processes, various technologies have been applied to the production of chemicals and fuels, food fermentation and waste water treatment. Over the past 25 years, there has been rapid progression in the production of liquid biofuels in context with alternative routes of bioconversion of biomass. There has been a great deal of development by researchers in those routes depending on the activity of plant cell wall degrading enzymes, as well as the conventional routes to bioethanol from corn, sugar beet, wheat or other cereal grains.
Soaring demand and limited supply of gasoline has resulted in recent drastic price hikes and this trend is expected to continue. Price and environmental concerns are resulting in increased awareness and demand for alternative fuel sources. The United States currently produces over 4.6 billion gallons of fuel ethanol at 102 plants using 1.7 billion bushels of corn each year and plans to increase rapidly in annual production capacity en route to 7.5 billion gallons in the next few years. Considering the current annual domestic gasoline consumption of 140 billion gallons, the biofuel of ethanol is only 3.2% of domestic fuel production necessary for automobiles. However, the fuel ethanol would be a short-term option to diversify fuel sources, not to mention its positive impact on the environmental and the greenhouse effects. For renewable fuels, the U.S. Department of Agriculture reported that every 1 Btu of petroleum fuel used to produce ethanol generates 13.2 Btu's, thereby greatly enhances domestic energy security.
Currently, ethanol is produced mainly from corn starch using the yeast of Saccharomyces Cerevisiae strains. To meet the future renewable fuels standard (RFS) requirement in the U.S., however, relatively inexpensive raw materials of celluloses such as hemicelluloses and lignocelluloses are seriously being pursued to further reduce production costs of the fuel ethanol. The Renewable Fuels Association (RFA) is targeting for 250 million gallons of the annual cellulosic ethanol production by 2012.
During the production of ethanol, ethanologenic microorganisms, such as mesophilic ethanologenic microorganisms, are able to grow and efficiently ferment sugars at pH's between 3.8-6.0 and temperatures from 82 to 95° F. Under ideal incubation conditions, microorganisms grow with basic nutrients, mainly comprised of water, carbon and nitrogen sources, phosphorus, and vitamins and minerals.
However, the growth of microbial cells is inhibited by many stress factors under industrial fermentation conditions, including physical stresses of temperature, osmotic pressure and plasmolysis, chemical stresses of alcohol inhibition, oxidation, acidity, toxicity and mutagenesis, and biological stresses of cellular aging, genetypic changes and competition from other microorganisms (Walker, G., Yeast Physiology and Biotechnology, John Wiley and Sons Ltd., United Kingdom, (1999)). Accordingly, it is necessary to find a way to promote the growth of microorganisms in order to achieve the maximal fermentation productivity.
Several technologies have currently been introduced to improve the fermentation process, especially for the production of fuel ethanol. Such a technology is disclosed in pending U.S. Patent Application Publication No. US 2002/0137154, for the use of acetaldehyde and other glycolic metabolites as nutrient additives. However, it may not be a practical alternative for an industrial fermentation process due to environmental and economic issues related to nutrients.
Other technologies, including the use of ultrasonic energy (U.S. Patent Application Publication No. US 2005/0136520), and addition of dicarboxylic acids (U.S. Pat. No. 6,569,670) for the improvement of bioconversion processes are more related to enzymatic hydrolysis reactions altering rheologies of fluid media. In addition, these technologies are not related to the improvement of the growth of microorganisms that is critical for the fermentation, especially under the industrial stressful environment.
Using infrared radiation, several technologies are disclosed to apply directly for industrial heating devices. U.S. Pat. Nos. 5,472,720 and 5,707,911 disclose the treatment of ceramic materials with infrared radiation, and the manufacturing of ceramic materials for infrared dryer and stabilizer, respectively. U.S. Pat. No. 5,542,194 also discloses far-infrared radiating ceramic materials mainly of SiC for heating apparatus, claiming excellent anticorrosivity and radiation capabilities. However, all these ceramic materials for industrial heating devices are not suitable for biological conversion processes due to their chemical and physical characteristics.
Therefore, there is a continued need for more effective technologies for improving the fermentation processes and subsequent improvement of bioconversion productivities, thus producing economic and environmental benefits. Accordingly, the object of the invention is to provide a method for improvement of the growth of microorganisms required for bioconversion processes and for reducing the cost of bioconversion products.